1) Field of the Invention
The present invention relates to a technology for performing coding on image data.
2) Description of the Related Art
With the advancement of the Large Scale Integration (LSI) technique and the computer technique, dynamic image coding typified by the Moving Picture Experts Group (MPEG)-2 and MPEG-4 has become increasingly common. With the MPEG-2 being applied to such fields as broadcasting and DVDs (Digital Versatile Discs), while the MPEG-4 being applied to portable telephones, portable video viewers, and the like, the digitization of dynamic images has become an indispensable technique today.
Image coding, such as motion compensation, motion detection, and discrete cosine transform, is a repetitive processing in which an identical process is repeatedly performed on subject image data. For such repetitive processing, the Single Instruction Multiple Data (SIMD) may be favorably employed. The SIMD, which was developed in line with the further sophistication of general purpose processor, advantageously realizes a simultaneous and high-speed processing when an identical process is to be performed on a plurality of data.
It is known to adopt the SIMD for image coding to achieve a high-speed processing (for example, see “A Fast Precise Implementation of 8×8 Discrete Cosine Transform Using the Streaming SIMD Extensions and MMXTM Instructions Version 1.0,” April 1999). As is known to those skilled in the art, the SIMD instruction, when employed in a Pentium (registered trademark) 3 processor manufactured by Intel Corporation, enables the completion of discrete cosine transform in fifty cycles in contrast to 970 cycles required in a conventional method which does not use the SIMD.
Meanwhile, it has been studied to achieve dynamic image coding which would allow the generation of high-quality image. A conventionally known such technique is rate distortion optimization which is generally utilized for motion detection and coding mode decision.
The technique of the rate distortion optimization is applied, for example, to motion estimation, scanning in DCT coefficient quantization, determination of quantization step sizes, and intra/inter mode decision (see, for example, Japanese Patent Application Laid-Open Publication No. 2003-230149).
However, in intra/inter mode decision utilizing the rate distortion optimization, for example, the quantity of codes generated through dynamic image coding and coding distortion caused thereby are used for the processing. Hence, in order to make an intra/inter mode decision it may be necessary to actually conduct coding process in each of the intra mode and the inter mode. Since coding process requires a long time, however, there may be a problem that the calculation cost becomes high.